Summary/Abstract Access to health insurance among the near elderly has increased dramatically in recent years due to the expansion of state Medicaid programs and subsidies for private coverage, creating the potential to improve the health and well-being of this population. Health insurance increases access to health care, and recent innovations in medical technology may disproportionally benefit this population due to their high prevalence of chronic health conditions and their poor health relative to younger adults. Very little evidence exists, however, on the effects of health insurance on health outcomes among people 45 to 64. This evidence is essential for understanding the extent to which the health care system is translating advances in health care technology into better health for older adults. The objective of this project is to understand how access to health care affects health among the near elderly. Our project has the following two specific aims: 1) to determine how health insurance affects health care use among the near elderly and; 2) to determine how health insurance affects the health of the near elderly. We will achieve these aims by conducting quasi-experimental analyses of longitudinal survey and administrative claims data exploiting geographic variation in the availability of subsidized health insurance to low-income near-elderly adults during the time period 2010-2016. While our analyses will generally take the form of a ?difference-in-difference? identification strategy, comparing changes over time in relevant outcomes between groups exposed to a coverage expansion relative to those not exposed, we will use several different approaches to examining the effects of policy-induced variation in exposure to health insurance, including examining differences between states that expanded their Medicaid programs as part of the broader expansions that started in 2014, examining states that expanded Medicaid coverage early to low income adults prior to 2014, and analyzing transitions into Medicare for both groups. By achieving these aims, we will provide some of the first evidence on the contemporary effects of health care access on health outcomes for older adults in the 45-64 age range. This evidence is crucial for understanding the extent to which the U.S. health care system is translating biomedical discoveries and advances in preventive care into improved population health, focusing on those who may benefit most from greater access to care. Our analyses will also provide new evidence on how different publicly funded programs, specifically Medicare and the under-65 programs of Medicaid and subsidies for private insurance, interact in the production of health.